THE PERIODICAL CICADA 


BY 
WM. J. GERHARD 


Associate Curator of Insects 


FIELD MUSEUM OF NATURAL HISTORY 


CHICAGO 
1923 


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PERIODICAL OR 
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THE PERIODICAL CICADA. 


FROM AN EXHIBIT IN FIELD MUSEUM OF NATURAL HISTORY, SHOWING THE VARIOUS STAGES 
OF THE INSECT AND THE INJURIOUS EGG-LAYING HABITS OF THE FEMALES. 


FIELD MUSEUM OF NATURAL HISTORY 
DEPARTMENT OF ZOOLOGY 
CHICAGO, 1923 


LEAFLET NUMBER 4 


The Periodical Cicada 


The Periodical or Seventeen-year Cicada, com- 
monly but improperly called the “seventeen-year 
locust,” is one of the most noteworthy insects found 
in North America. Its sudden appearance at inter- 
vals in large numbers in different parts of the eastern 
United States, the indescribable din caused by the 
multitude of singing males, and the conspicuous evi- 
dence of the damage the females do to deciduous trees, 
invariably arouse widespread attention and much fear 
concerning its destructive habits. 

The Periodical Cicada is a true bug and, like the 
other members of the order Hemiptera, has a jointed 
beak fitted for piercing the tissue of plants. The 
name locust, so commonly applied to it, is improper, 
because almost since the beginning of history it 
has been used to designate wholly different insects, 
namely, grasshoppers, which have biting mouth-parts 
and which are not closely related to cicadas. The use 
of the same name for two dissimilar insects, no doubt, 
is the result of confusing the cicadas with the devas- 
tating locusts of the old world and the destructive 
locusts or grasshoppers of the United States. 

Not only is this insect noteworthy on account of 
its periodic appearance in immense hordes, but it is 
remarkable for the extraordinary duration of its life 
in the larval and pupal stages. In the Northern 
States its immature stages extend over a period of 
seventeen years; in the South, thirteen years are 


[41] 


2 FIELD MUSEUM OF NATURAL HISTORY 


required for its underground existence. It is the 
only insect that is known to live for so long a period. 
The sound-producing organs of the adult male are 
likewise wholly different from those of other insects, 
in no way resembling the stridulating apparatus of 
grasshoppers, katydids and crickets. 


Like most insects, the Periodical Cicada passes 
through four stages during its life cycle, namely, the 
egg, larval, pupal and adult stages. Although some 
of the facts of the life-history were known to the 
early colonists, it was only during the latter half of 
the last century that much progress was made in 
solving many of the problems concerning this inter- 
esting cicada. Thus, for a long time it was difficult 
to account for the appearance of various broods in 
different sections of the country at intervals shorter 
than the customary seventeen-year period. The ex- 
planation became simple when it was ascertained that 
there were two races of this insect, one in the North- 
ern States requiring seventeen years for its life cycle, 
a southern one developing through all of its stages in 
thirteen years. 


On account of the difference in the duration of the 
life of the northern and southern races, at one time 
it was thought that there were two species of the 
Periodical Cicada in America. For this reason dif- 
ferent specific names were assigned to them. A name 
was also proposed for the small, dwarfed individuals 
that are found among nearly every brood. But as no 
constant, structural characters have been found to 
separate the three so-called species, entomologists 
now consider them to be one species, which they 
designate as Tibicina septendecim, with a southern 
race, tredecim, and a small form, cassini. 


By means of the many, scattered notes and records, 
extending back over two hundred years, and the more 


[ 42] 


THE PERIODICAL CICADA 
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Distribution of the broods of the 17-year race of the 
Periodical Cicada (after Marlatt). 


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Distribution of the broods of the 13-year race of the 
Periodical Cicada (after Marlatt). 


[43] 


4 FIELD MUSEUM OF NATURAL HISTORY 


recent, careful observations, it has become possible 
to trace out thirty broods of the Periodical Cicada. 
Seventeen broods belong to the northern race; thir- 
teen to the southern. These broods vary greatly in 
the number of individuals and in the range of their 
distribution. For example, Brood XI (1920) is very 
small and appears only in a few sections of Massachu- 
setts and Connecticut, whereas Brood X (1919) is 
recorded from at least fourteen states, in four of 
which, namely, Indiana, Ohio, Maryland and _ south- 
eastern Pennsylvania, it appears in dense swarms. 
Northern Illinois is within the range of only one 
large or dense brood, and that is the rather compact 
Brood XIII, which was so much in evidence during the 
summer of 1922. With the exception of a few records 
of individuals in some other states, this brood is 
distributed over the northern half of Illinois, eastern 
Iowa, southern Wisconsin and Michigan and north- 
western Indiana. 


The two maps: on the preceding page indicate the 
distribution of all the broods of the two races. It will 
be noted that the range of the two races overlaps for a 
short distance, particularly in southern Missouri, Ken- 
tucky, Tennessee, Illinois and Indiana. If the differ- 
ence in the duration of the immature stages of the two 
races were wholly due to climatic conditions, it would be 
natural to expect to find a gradual decrease in the time 
of development of the northern race as it approaches 
the northern limits of the southern race. This, how- 
ever, is not the case. Seemingly the time of develop- 
ment, while no doubt originally influenced by climatic 
conditions, has become fixed for the species or race as 
a whole and is now not permanently modified by 
slight differences in temperature. That the duration 
of the life of this cicada is sometimes either acceler- 
ated or retarded is quite evident, for not infrequently 


[44] 


THE PERIODICAL CICADA 5 


a few adults emerge a year before the main brood is 
due, or they may appear a year later. 

To account for the existence of the various broods 
today, the plausible theory has been advanced that 
originally, many centuries ago, there was but one 
brood for each of the two races and that they ap- 
peared throughout their entire range once every sev- 
enteen or thirteen years. But as accelerated or be- 
lated individuals increased in number, extended their 
range and resumed their normal life cycle, there were 
started the various broods that are now recognized. 
According to this hypothesis, if the breeding places do 
not become too limited and no other detrimental fac- 
tors arise, the different broods will increase to such an 
extent in the distant future that this insect will appear 
every year throughout its entire range. 


The newly hatched larve, or young, of the Periodi- 
cal Cicada are pale, minute, active creatures with 
thick forelegs well-fitted for digging and a jointed 
beak well-suited for piercing small roots. On emerg- 
ing from the egg, which will be described later, the 
young drop lightly to the ground and work their way 
into the soil for a short distance. Near some rootlet 
each larva encloses itself in a little, isolated, earthen 
cell which is enlarged as the young increases in size. 
It is not probable that they move about in the ground 
for any great distance, but just how they really pass 
this long, dark period of their life is not known and 
obviously is difficult to ascertain. Since their cells 
are nearly always found in close contact to a root or 
rootlet, it is believed that the immature cicadas feed 
mainly upon the juices of small roots. The depth to 
which the larve burrow varies from six to twenty- 
four inches. There are, however, records of some that 
were found four feet or more beneath the surface of 
the soil. During their long, subterranean existence 


[45] 


6 FIELD MUSEUM OF NATURAL HISTORY 


they grow slowly and moult or shed their skin at in- 
tervals of several years. Some time after the fourth 
moult, when the larve (of the northern race) are 
about twelve years old, they change into the first of 
their two pupal stages. 


The pup of the Periodical Cicada, unlike those of 
the majority of insects, rather closely resemble the 
larve. They likewise are quite active and continue 
to feed upon the juices of roots. Early in the spring, 
or during the latter part of April, a few months less 
than seventeen years after the young of the northern 
race began their subterranean life, the pups, seem- 
ingly all of them at the same time, burrow upward 
toward the surface of the ground. At first the exit 
burrows or cells may end just below the surface, 
under logs, stones, chips, or leaves; but under certain 
conditions the pupe erect tube-like chimneys or tur- 
rets of clay that extend from two to six inches above 
the ground. 

An astonishingly large number of larve and finally 
pupz sometimes inhabit a limited area of the soil. As 
many as twenty-five chimneys or turrets have been 
found on one square foot of ground, and nine thou- 
sand burrow exits have been counted under one tree. 


The exodus from their burrows occurs generally 
after sundown during the latter part of May and the 
fore part of June. During one evening myriads of 
pup, as if impelled by an irresistible force, leave 
their burrows and turrets and climb up on any nearby 
object. Some crawl up on plants less than a foot in 
height, while others may ascend trees for a distance 
of fifteen or more feet. On reaching a favorable 
spot, they rest quietly for a short period, their thick, 
front legs clinging tightly to their support. Shortly 
after it has become dark, the interesting transforma- 
tion begins. A longitudinal slit first appears along 


[46] 


THE PERIODICAL CICADA 7 


the middle of the forepart of the pupa’s back. This 
opening gradually widens as the pale adult slowly 
emerges and leaves the empty pupal skin attached to a 
leaf, twig or branch. 


The freshly emerged adults are rather ghostly 
creatures, soft, flabby, creamy white in color, with 
reddish compound eyes and two, black, rectangular 
spots on their back just behind the head. At first 
the wings are merely little, wrinkled, whitish pads 
with an orange tinge at their base, but they soon ex- 
pand to their final size. The entire body then be- 
gins to harden and to assume the characteristic color 
of the species. A few hours after sunrise on the 
morning following their transformation, the adult 
cicadas are ready to commence their short but active 
career, lasting only from four to six weeks. 


Until a comparatively recent date it was believed 
that no food was taken by the Periodical Cicada in 
the adult stage. It is now known, however, that it 
does feed upon the sap of trees,' the branches of which 
it pierces by means of its beak. Whether the taking 
of food is really essential for mating and egg-laying 
is still an open question. For obtaining liquid nour- 
ishment its mouth-parts are well fitted. Instead of 
having biting jaws, it possesses a jointed, beak-like 
lower lip which encloses fine, elongated, stiff, piercing 
organs that, with their beak-like sheath, convey the 
sap to the mouth cavity. Under favorable conditions, 
this insect could readily pierce the human skin by 
means of its beak, but apparently it rarely or never 
attempts to protect itself in such a manner. 


The egg-laying habits of this cicada are of consid- 
erable interest, and to them is due most of the dam- 
age caused by this insect. The female inserts her 
eggs in the twigs and branches of trees by means of 
a strong, curved ovipositor which extends from the 


[47] 


8 FIELD MUSEUM OF NATURAL HISTORY 


underside of the abdomen. The main part of the 
ovipositor consists of three, horny pieces, two of which 
are serrated and spear-shaped at the tip, and by a 
backward and forward movement are able to make 
a series of punctures in hard wood. Despite a belief 
to the contrary, the ovipositor is not a sting, and it is 
doubtful whether it is ever used as a means of defense. 


The eggs of the Periodical Cicada are whitish, 
cylindrical and about one-twelfth of an inch in length. 
They are inserted just below the surface and are in- 
clined forward at an angle of 45 degrees. With her 
ovipositor the female makes a series of punctures, 
generally on the under side of the twig, about half an 
inch in length, and in them she then lays a longitudinal 
row of eggs in pairs. Without changing her position 
on the twig, she makes another series of punctures 
along side of the first, so that finally each egg nest in 
the twig consists of two more or less parallel rows of 
eggs, from ten to eighteen in number and separated 
by a thin partition. Beginning toward the base of 
the twig, which commonly is one of the previous 
year’s growth, she works toward the tip, or occasion- 
ally toward the base. Sometimes the egg nests are so 
close together that they appear to be continuous. 
One twig after another is supposed to be pierced in 
the manner described until the female has laid her 
batch of eggs, which may number from two to six 
hundred. 


The eggs are laid in a large variety of trees, bushes, 
and sometimes in herbaceous plants. Oak trees, 
either young or old, seem to be preferred, possibly 
because in most woodland tracts they predominate, 
and, therefore, are the most accessible. Pine trees 
appear to be exempt, the gummy sap exuding from the 
punctures, no doubt, being detrimental to the hatch- 
ing of the eggs. 


[48] 


THE PERIODICAL CICADA 


1. Egg. 5and 6. Body of males. 
2. Newly hatched larva. (Showing sound organs at A) 
8. Full grown larva. 7. Body of female. 
(Fourth stage) (Showing ovipositor) 
4. Pupa (second stage). 8. Adult female. 
(Very similar to first stage) 9. Egg nests in twig. 


(Figs. 1, 2 and 3 greatly enlarged, after Marlatt; figs. 4-9 slightly reduced.) 


[49] 


10 FIELD MUSEUM OF NATURAL HISTORY 


The results of the cicada’s egg-laying habits vary 
with different trees. The oaks show the effects most 
conspicuously; the leaves beyond the first punctures 
_ turn brown, and many of the twigs become so weak 
that they are broken off by the wind. Under the less 
hardy oaks the ground is sometimes almost covered 
with dead terminal twigs. A few weeks after a 
large brood has emerged, tracts of oak woodland ap- 
pear as though they had been scorched by a forest 
fire. But some trees withstand the effects of the 
punctures fairly well, though the egg nests are prone 
to leave scars that eventually produce a weak spot 
in the growing branch. 


The Seventeen-year Cicada fortunately appears 
mainly and most abundantly in woodland tracts, 
places where its injurious habits do not result in an 
appreciable, monetary loss. It likewise does not fly 
far from its breeding grounds. Nevertheless, it often 
does much harm to fruit trees. This is particularly 
the case wherever orchards and nurseries are located 
near wooded areas in which the cicadas may be nu- 
merous. Not only is nursery stock sometimes badly 
injured, but frequently young trees die from the re- 
sults of the egg punctures. 


A few days after a large brood of cicadas has 
emerged from the ground, the air resounds with the 
peculiar, whirring noise caused by the countless 
males. It is only the male that is capable of making 
the characteristic buzzing sound; and no other in- 
sects, except those belonging to the cicada family, 
have a similar musical apparatus. The sound organs 
occupy nearly the entire basal segment of the abdo- 
men. The most conspicuous of these organs are two, 
covering flaps or opercula, visible only from below, 
and two tense, ribbed drum-like membranes which 
are vibrated by two powerful muscles. By raising 


[50] 


THE PERIODICAL CICADA ll 


and lowering the abdomen, thereby changing the posi- 
tion of the opercula, as well as in other ways, the 
nature of the song is changed at will. So distinctive 
is the sound produced by the various species of 
cicadas, that a student learns to recognize many of 
them by their song alone. 


The family Cicadidez, of which the Periodical Cicada 
is the most noteworthy member, belongs to the order 
Hemiptera, which comprises the true bugs or those 
insects having a jointed beak fitted for piercing and 
sucking. The family is well represented throughout 
the tropical and temperate regions: of both hemis- 
pheres, over eight hundred species having been 
described. Of this number one hundred and thirteen 
are listed from America north of Mexico. All of the 
females lay their eggs in the tissues of plants or trees; 
all of the males have the complex, sound organs, and 
are considered to be the noisiest insects in the world; 
but, with the exception of the Periodical Cicada, so 
far as known, not one of them requires more than two 
years for its development from the egg to the adult 
stage. The Dog-day Harvest-fly or Lyreman is one of 
the common cicadas that is heard every summer. As 
it is two-brooded, the adults appear every year. 


The cicadas are fairly large, four-winged insects, 
with a blunt head, three-jointed beak arising near 
the base of the lower surface of the head, prominent 
compound eyes, three simple eyes or ocelli, and an ab- 
domen consisting of six segments. The front legs 
are much thickened and armed with a spine beneath. 
The wings are of a similar texture throughout, and 
when at rest extend roof-like over the body. In the 
tropics many of the species are brightly colored, but 
in the United States they are mostly greenish marked 
with red and black. 


{ 51] 


12 FIELD MUSEUM OF NATURAL HISTORY 


There is no conclusive evidence apparently that the 
immature Periodical Cicada does very much injury to 
plants or trees during the long period that it feeds 
upon the juices of small roots. It is, therefore, only 
in exceptional cases, or in very limited areas, that it 
might prove desirable to destroy the young. Accord- 
ing to Dr. Marlatt, the most satisfactory method of 
killing the larve is the use of bisulphide of carbon in- 
jected into the soil where it is known they are quite 
numerous. 


In the adult stage the females unquestionably are 
very harmful to various trees and shrubs, though the 
damage they do is probably not nearly so extensive 
as is generally supposed. On oak trees, at least, the 
results of their egg-laying habits are much in the 
nature of a pruning. But in orchards and nurseries 
the trees are sometimes injured so severely that some 
means of protecting or saving them and destroying 
the cicadas must be adopted. 


On account of the myriad of individuals over a wide 
area and the short life of the adults, the usual methods 
of destroying noxious insects are not always practi- 
cal. The use of repellents to prevent the females from 
ovipositing has likewise not met with much success. 
When the adults emerge near orchards or nurseries, 
young fruit trees should, if possible, be protected by 
netting, and the cicadas resting thereon should be col- 
lected and killed every morning and evening, when 
they are somewhat sluggish. As the egg nests or scars 
often serve as openings for other destructive insects, it 
is quite essential to take proper care of young injured 
trees. In limited areas, like parks and yards contain- 
ing shade trees and shrubbery, the emerging and 
adult cicadas can be readily killed by spraying them 
with a strong kerosene emulsion. Even the pup are 
not immune to an emulsion of kerosene, soap and 


[52] 


THE PERIODICAL CICADA 13 


water. Since the various broods are known to appear 
during a definite year in different places, it is obviously 
unwise to plant nursery stock or orchards near wood- 
land when this insect is soon due. 


Although the Periodical Cicada may not appear to 
be decreasing in number to the casual observer, there 
is sufficient evidence to indicate that it is not nearly 
so abundant in many places as it was years ago. Mites 
and other insects prey upon it in its various stages, 
and very many of the rather helpless adults are de- 
voured by birds, especially the English sparrow. But 
the most potent factors that are reducing their num- 
ber are the diminishing woodland areas and the clear- 
ing of land for cultivation. It is, therefore, not im- 
probable that in the distant future this long-lived in- 
sect may be exterminated by the agricultural devel- 
opment of the country. 


Wm. J. GERHARD, 
Associate Curator of Insects. 


[53] 


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